Golf balls are generally coated with paint In order to look beautiful or to prevent damage to the ball surface. The paint layer is composed of an enamel paint containing pigments such as titanium oxide, etc., and a clear paint containing no pigments, formed on the enamel paint, or a clear paint only.
Hitherto, an organic solvent based two-package reaction type urethane paint has been used for the paint for golf balls. Also, an epoxy paint is often used as primer. The use of the conventional paint has problems in safety and working environment, because an organic solvent is used.
On the other hand, in recent years, so-called non-enamel golf balls, coated only with clear paint, tend to gain popularity for the reason of good luster and tone. However, they have a defect to deteriorate the golf ball cover surface and to reduce adhesion between the cover and the paint, because sun light penetrates through the paint layer and directly irradiates the cover when non-enamel golf ball is exposed outdoors. Consequently, it is required more than ever to improve the adhesion between the paint and the cover.
To solve the above two problems, that is, to eliminate the use of organic solvents and to improve the adhesion between the paint and the golf ball cover, a water dispersed urethane paint has been proposed in Japanese Patent Kokoku Publication Hei-2(1990)-11095. The paint proposed in the Utility Model Publication solves problems associated with the use of organic solvents and improves the adhesion between the golf ball cover and the paint layer, to some extent. It is, however, desired to further improve adhesion, durability and strength of the paint layer. Also, the paint of the Utility Model Publication employs polyfunctional ethyleneimine (aziridine) compounds as crosslinking agents, which, however, are effective for solving the problems to some extent but not satisfactorily. Further the ethyleneimine is a substance having mutagenicity and is limited in use.